Question 19
Two positive integers $a,b$ have highest common factor 4 and lowest common multiple 720. Given $a\le b$, how many pairs $(a,b)$ are there?
Answer format: enter one whole number without units; leading zeros are optional. The source answer sheet uses four digits (for example, 7 is shaded as 0007).
Answer format: enter one whole number without units; leading zeros are optional. The source answer sheet uses four digits (for example, 7 is shaded as 0007).